1. Field of the Invention
The present invention relates to known sensor elements that serve as exhaust-gas sensors, for example, in particular as lambda probes that are widely used in motor vehicles. However, the present invention can also be applied to other types of sensor elements, for example, to sensors for detecting other gaseous components of exhaust gases, and also to particle sensors or the like. In particular, the present invention relates to a sintered or sinterable ceramic sensor element that is produced, for example, by assembling individual, in some instances imprinted ceramic green films, in particular by stacking them one upon the other.
2. Description of the Related Art
In particular, the sensor element of the type described above includes at least one electrical, electrochemical and/or electronic functional element in a first end region of the sensor element, generally a first end region facing the exhaust gas. The sensor element's ability to be electrically powered is provided here by a contact area on the outer surface thereof in a second region, typically one facing away from the exhaust gas.
The sensor element's ability to be electrically powered is provided here by an electrical connection of the functional element with the contact area that includes a conductor in the interior of the sensor element that essentially extends in the longitudinal direction of the sensor element and a leadthrough that essentially extends orthogonally to the longitudinal direction of the sensor element, in particular in the vertical direction. Sensor elements of this kind are known, for example, from the German Patent Application DE 10 2006 055 797 A1.
During operation and manufacture of the sensor element, high temperature and chemical resistances are required for the electrical connection. Therefore, noble metals, such as platinum or the like, are widely used. Since such noble metals are relatively expensive, efforts are generally directed to reducing the quantity of material used.
This type of miniaturization of the electrical connection is limited in that, at a specified resistance, the total resistance is all the greater, the smaller the particular lead cross sections are. Resulting voltage drops, respectively power losses and/or signal distortions can only be tolerated within predefined limits.
In particular, such a total resistance limit of this electrical connection of the functional element, in particular of a heating resistor, with the contact area is to be seen within the range here of 1 to 4 ohms at 20° C., in particular within the range of 2 to 3 ohms at 20° C.